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Ice to Iron

Project Description

Glacial sediments are important sources of nutrients to the ocean, especially the Southern Ocean where nutrient-stimulated changes in the biological pump plays a large role in global carbon cycling. Marine terminating glaciers are sources of abundant terrigenous sediment particles which are transported different distances depending on their grain size and ocean circulation. They dissolve and chemically exchange with seawater, so that the finest glacial sediment can be an important source of limiting nutrients for open ocean phytoplankton [1]. Southern Ocean islands are experiencing some of the fastest rates of deglaciation on the planet [2] with some glaciers on South Georgia retreating 14 km in the last 40 years. If glaciers around Southern Ocean islands continue to retreat the supply, grainsize and chemistry of glacial sediment will change dramatically. How this will affect marine nutrient levels, stoichiometry and the trophic web is at present unclear, but as the Southern Ocean islands are important areas for productivity, higher predators and have economically important fisheries, understanding these consequences is critical for future planning for sustainable management.

This project will use the ocean around South Georgia as a “natural laboratory” to examine the controls on particle input, transport, and dissolution and in the Southern Ocean. Unlike large particles which are rapidly sedimented, fine particulate matter, called glacial flour, is added into a fresh water layer at the surface and depending on physical oceanographic conditions can stay longer in the water column and be transported to nutrient deficient areas of open ocean. These fine sediments at the sea-surface have a distinctive blue colour and can be easily identified by satellite imagery. This project will map these sediments and investigate grainsize, mineralogy and exchange rates to understand how they become biologically available, a poorly understood process important for marine nutrient cycling [3].

The student will use remote sensing and geochemical techniques to constrain terrigenous particles on marine nutrient chemistry. At South Georgia most glacial flour originates from the glaciers on the northern side of the island, prevailing currents transport the sediments northwest to the areas of greatest biological productivity. In the 2019/2020 season BAS scientists will conduct spectral analysis of spectral flour in-situ near the outflow of the Neumayer Glacier in Cumberland Bay, this will be the first known collection of glacial flour spectra and will provide a solid basis for future remote sensing analysis. SG Govt will collect water samples to support the project. The extant of dissolution of these particles, and therefore nutrient addition to seawater, is likely to be dependent on particle size and composition, which can be constrained from field samples. The chemistry of the sediment will place additional constraints on the source and advective pathways of particles of different grain sizes. The amount of dissolution and the stoichiometry of nutrients released to seawater will be examined by comparing sediment and seawater samples and/or in laboratory experiments.

Funding Notes

UK and EU students who meet the UK residency requirements will be eligible for a full NERC studentship. Students from EU countries who do not meet the residency requirements may still be eligible for a fees-only award. More information can be found in the UKRI Training Grant Terms and Conditions
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[1] Gerringa, L.J.A., Alderkamp, A-C., Laan, P., et al. Iron from melting glaciers fuels the phytoplankton blooms in Amundsen Sea (Southern Ocean): Iron biogeochemistry. Deep-Sea Research II –76 (2012) 16–31. https://doi.org/(...)6/j.dsr2.2012.03.007
[2] Cook, A., Poncet, S., Cooper, A., Herbert, D., & Christie, D. (2010). Glacier retreat on South Georgia and implications for the spread of rats. Antarctic Science, 22(3), 255-263. doi:10.1017/S0954102010000064
[3] Jeandel, C., Oelkers, E.H. (2015) The influence of terrigenous particulate material dissolution on ocean chemistry and global element cycles. Chemical Geology 395, 50-66.

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